1. Field of the Disclosure
Embodiments of the present disclosure generally relate to transistor gate structures and methods of forming the same.
2. Description of the Related Art
A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one of the transistor's terminals changes the current through another pair of terminals. For example, a voltage applied to a gate of a transistor affects the current flowing between a source terminal and a sink terminal of the transistor. The threshold voltage of the gate at which current flows between the source terminal and the sink terminal is the flat band voltage (VFB). In conventional metal-oxide-semiconductor FETs (MOSFETs), the threshold voltage often fails to meet the desired value. In some cases, electrode stacks are chosen according to work function to provide the desired characteristics, but this often does not work. Moreover, threshold voltage shifts can vary significantly from desired values resulting in undesired shifts which affect device performance.
Thus, there is a need in the art for a method and apparatus for flatband voltage tuning of high-k field effect transistors.